
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无缝滚动</title>
<style type="text/css">
body,div,ul,li{margin:0;padding:0;}
body{background:#052D01;font:12px/1.5 arial;}
#box{position:relative;width:210px;height:700px;border:1px solid #5E8743;margin:20px;}
#box div{position:absolute;top:50%;left:50%;width:160px;height:570px;overflow:hidden;margin:-285px 0 0 -80px;}
#box .up,#box .down{position:absolute;left:50%;width:48px;height:48px;z-index:10;cursor:pointer;overflow:hidden;margin-left:-24px;text-indent:-9999px;background:url(img/arrow.jpg) no-repeat;}
#box .up{top:10px;background-position:0 0;}
#box .down{bottom:10px;background-position:0 bottom;}
#box ul{position:absolute;width:160px;}
#box li{width:160px;height:190px;list-style:none;text-align:center;}
#box a{color:#fff;font-weight:700;text-decoration:none;}
#box img{width:156px;height:156px;display:block;margin-bottom:5px;border:2px solid #ccc;}
</style>
<script type="text/javascript">
//获取id
function $ (id)
{
	return typeof id === "string" ? document.getElementById(id) : id;	
}
//获取tagName
function $$ (elem, oParent)
{
	return (oParent || document).getElementsByTagName(elem);	
}
//获取class
function $$$ (className, oParent)
{
	var aClass = [];
	var reClass = new RegExp("(//s|^)" + className + "($|//s)");
	var aElem = $$("*", oParent);
	for (var i = 0; i < aElem.length; i++) reClass.test(aElem[i].className) && aClass.push(aElem[i]);
	return aClass
}
//初始化对象
function Roll ()
{
	this.initialize.apply(this, arguments)	
}
Roll.prototype =
{
	initialize: function (obj)
	{
		var _this = this;
		this.obj = $(obj);
		this.oUp = $$$("up", this.obj)[0];
		this.oDown = $$$("down", this.obj)[0];
		this.oList = $$$("list", this.obj)[0];
		this.aItem = this.oList.children;
		this.timer = null;
		this.iHeight = this.aItem[0].offsetHeight;
		this.oUp.onclick = function ()
		{
			_this.up()	
		};
		this.oDown.onclick = function ()
		{
			_this.down()
		}	
	},
	up: function ()
	{
		this.oList.insertBefore(this.aItem[this.aItem.length - 1], this.oList.firstChild);
		this.oList.style.top = -this.iHeight + "px";
		this.doMove(0)
	},
	down: function ()
	{
		this.doMove(-this.iHeight, function ()
		{
			this.oList.appendChild(this.aItem[0]);
			this.oList.style.top = 0;	
		})
	},
	doMove: function (iTarget, callBack)
	{
		var _this = this;
		clearInterval(this.timer)
		this.timer = setInterval(function ()
		{
			var iSpeed = (iTarget - _this.oList.offsetTop) / 5;
			iSpeed = iSpeed > 0 ? Math.ceil(iSpeed) : Math.floor(iSpeed);
			_this.oList.offsetTop == iTarget ? (clearInterval(_this.timer), callBack && callBack.apply(_this)) : _this.oList.style.top = iSpeed + _this.oList.offsetTop + "px"
		}, 30)
	}
};

window.onload = function ()
{
	new Roll("box");
};
</script>
</head>
<body>
<div id="box">
    <span class="up">up</span>
    <span class="down">down</span>
    <div>
        <ul class="list">
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            <li><a href="javascript:;"><img src="img/wf3.jpg" />Maui Stables</a></li>
            <li><a href="javascript:;"><img src="img/wf4.jpg" />Code Rebel 3.0</a></li>
            <li><a href="javascript:;"><img src="img/wf5.jpg" />SecurityPro Shop</a></li>
        </ul>
    </div>
</div>
</body>
</html>
